Printing error detection

ABSTRACT

There is disclosed a device, method and program, wherein the method comprises detecting a power increase, during which power usage increases by at least a threshold amount over an expected power usage during movement of a printer carriage over a print medium along a scan axis. The increase method further comprises detecting a location of the printer carriage at a time of the detected power usage increase and determining, based on the detected location of the printer carriage, whether the print medium is damaged.

BACKGROUND

Many printers deposit print material on a print medium. Printing may becarried out by passing the print medium along a printing path. A printercarriage may be passed over the print medium at a print location along ascan axis. The scan axis may be perpendicular to the direction ofmovement of the print medium along the printing path. Print media may bemade of materials such as paper, Mylar, vinyl and textiles, for example.Print media may have different thicknesses.

BRIEF DESCRIPTION OF DRAWINGS

Examples will now be described, by way of non-limiting example, withreference to the accompanying drawings, in which:

FIG. 1 is a flowchart of an example of a method of determining whetherprint medium is damaged in accordance with some examples;

FIG. 2 is a simplified schematic of an example of an apparatus fordetermining whether a print medium is damaged in accordance with someexamples;

FIG. 3 is a flowchart of a further example for method of determiningwhether print medium is damaged in accordance with some examples;

FIG. 4 is a flowchart of a further example of a method of determiningwhether a print medium is damaged in accordance with some examples;

FIG. 5 is a simplified schematic of a further example of an apparatusfor determining whether a print medium is damaged in accordance withsome examples; and

FIGS. 6a and 6b are graphs showing how a usage readings relating tonormal printing and when damage has occurred, respectively.

DETAILED DESCRIPTION

Print media used in various forms of printing, for example, dyesublimation printing, may vary in thickness. A trend recently is towardsusing print media of lower grammage (grams per square metre). Thesethinner print media may offer lower costs per copy and may allow forlonger uninterrupted printing. As print media becomes thinner tendenciestowards wrinkling and ink-media interactions including paper expansionmay become more common, both of which may lead to contact between theprint medium and the printer carriage. Such contact may be described asa “crash”, for example. In some examples the print media may be so thinthat a printer may continue to print even when a print media is damaged.This may lead to print material waste, printer damage, or furthersubsequent damage to the print medium.

In some examples, there is provided a method of detecting variations inthe power used to move a printer carriage, during printing, whencompared with expected power usage values. The variations may then belinked to the location of the printer carriage and, if the printercarriage is outside a predefined print zone at the time of thevariation, the variation may be deemed not to be the result of damage tothe print medium. If the printer carriage is inside the predefined printzone at the time of the variation, the variation may be deemed toindicate damage to the print medium. This method may help to eliminatefalse positives when other power usage variations are detected, such asduring acceleration of the printer carriage.

In some examples, as shown in FIG. 1, a method is provided comprisingdetecting S101 a power increase. A power increase (such as a “spike” or“jump” in power usage) may occur when power usage increases by at leasta threshold amount over an expected power usage during movement of aprinter carriage over a print medium along a scan axis. The method mayfurther comprise detecting S102 a location of the printer carriage at atime of the detected power usage increase. The method may furthercomprise determining S103, based on the detected location of the printercarriage, whether the print medium is damaged.

During a print movement (for example the movement of a printer carriagefrom one side of the print medium to the other, sometimes referred to asa swath) the power used to move the printer carriage may be continuouslymonitored. An expected power usage for a movement of the printercarriage may be predetermined. This may be described as a power usageprofile over time for a printer carriage movement. A power increaseoccurs when the difference between the actual power used and theexpected power usage differ by at least a threshold amount.

A power increase may also be described as a power variation ordifference, as it is an indicator which relates to the expected powerusage. An expected power usage may for example be based on the actualmeasured power usage of the last print movement, or based on calculatedpower usage for a given print movement.

The power used to move the printer carriage may be proportionate to theresistance to movement result from many factors including the weight ofthe printer carriage, friction between the moving components of theprinter, and, in the event of contact between the printer carriage andthe print medium, the resultant additional resistance. In some examples,at the end of each print swath the power used to move the carriage alongthe scan axis is evaluated. If a peak is detected when the carriage ispassing over the substrate edges it may be inferred that a crash hasoccurred. If this peak is maintained or increases during the print swaththen it may be likely that a tear has occurred, and part of thesubstrate is being moved by the carriage.

In some examples the power usage is monitored during movement of theprinter carriage and linked to the position of the printer carriageduring the movement. Carrying out the continuous monitoring of the powerusage and linking this to the position of the printer carriage on thescan axis may allow for a more accurate profiling of the power usage andmovement of the printer carriage for each printing pass (swath). In someexamples the location of the printer carriage may be determined at thetime that a power increase is detected.

In some examples the method may further comprise, when the position ofthe printer carriage corresponds to an edge of a print zone at the timeof the detected power usage increase, determining that the print mediumis damaged. The print zone may for example correspond to the areacovered by the print medium and edges of the print zone correspond tothe sides of the print medium. Contact between the printer carriage andthe print medium may be more likely to first occur at the edges of theprint medium, particularly when the print medium does not lie flat overthe surface beneath. Damage to the print medium may therefore be likelyto begin when the printer carriage passes thereover. Consequently, apower usage variation, or increase, which occurs when the printercarriage is at or near the edge of the print medium may be indicative ofa crash and therefore damage to the print medium.

A position corresponding to an edge of the print zone may be at orsufficiently near the edge of the print medium to indicate such a crash.For example, print medium may move slightly when first coming intocontact with the printer carriage, before being folded, creased orripped, such that the power usage increase is caused. Therefore, thepower usage increase may be detected at or slightly after the printercarriage passes over the position of the edge of the print medium.

In some examples, as shown in FIG. 2, there is provided a device, forexample a damage determining device 10, comprising a power monitor 100to detect a power increase, during which power usage increases by atleast a threshold amount over an expected power usage during movement ofa printer carriage over a print medium along a scan axis. The damagedetermining device 10 may be included as part of a printer carriage ormaybe a separate device to the printer carriage. The power monitor 100may further continuously monitor the power usage associated with movingthe printer carriage over the print medium along a scan axis duringprinting.

The device may further comprise a locator 110 to detect a location ofthe printer carriage at the time of the detected power increase. Thedevice may further comprise a damage determiner 120 to determine, basedon the detected location of the printer carriage, whether the printmedium is damaged. The damage determiner 120 may determine that, if thedetected location is within the print zone, it is likely that the printmedium is damaged. If the detected location is outside the print zonehowever the damage determiner 120 may determine that the print medium isnot damaged. If a power increase as described above occurs within theprint zone, it may be likely that this is due to a collision of theprinter carriage with the print medium. If however a power increase asdescribed above occurs outside the print zone it is possible that thepower increase may relate to acceleration of the printer carriage and,more significantly, with no print medium outside the print zone it isless likely that this has resulted in damage to the print medium.

In some examples the device may further include an optical sensor 130,such as a camera or other visual inspection device, to inspect the printmedium for damage. The optical sensor may be located on the printercarriage to allow visual inspection of the print medium during asubsequent print pass. The optical sensor 130 may be used to confirmdamage detection, in which case the printer may perform a scan using theoptical sensor 130, which may be embedded in the carriage, on thefollowing pass. If substrate is found during the scan, then, its startand end positions (on this scan axis) may be compared to expectedpositions or positions scanned previously during media loading, todetermine the presence of a tear. In the case that no tear is foundprinting may continue normally with minimal throughput loss since onlyone extra pass to carry out the visual inspection may be used.

In some examples, as shown in FIG. 3, the method (wherein S101 to S103in FIG. 1 correspond to S301 to S303 in FIG. 3) may further comprise, atthe end of each print carriage movement, evaluating S304 the power usageover the printer carriage movement. In some examples the evaluation maybe carried out if no power increase is detected and may not be carriedout if a power increase is detected. In the event no power increase(power variation) is detected, the evaluated power usage may be used asthe expected power usage for the following print movement or othersubsequent print movements.

Further in some examples the method may further comprise, based on thepower usage evaluation, determining S305 whether an increase in frictionis detected during printer carriage movement. Incremental smallincreases in friction associated with movement of the printer carriagemay occur due to standard usage of the printer.

To reduce or eliminate the influence of the friction increase it may bepossible to iteratively update the expected power usage values to takethe corresponding power usage increase, due to the additional friction,into account. Taking these into account, it may be possible to calibratethe expected power values more accurately for each movement of theprinter carriage. Following detection of damage to the print medium, avisual inspection may be carried out to establish the extent of thedamage.

In some examples, the method may further comprise applying a decayfilter S306 to the expected power usage to adjust the threshold powerusage increase amount. With each print movement, it may be possible toassess an appropriate threshold, for the change in the power usagerelative to the expected power usage, to detect increases indicative ofcontact between the printer carriage and the print medium. A decayfilter, used to adjust the threshold, may be applied using the followingequations.

Power_(Average)(t+1)=Power_(Average)(t)·α+Power_(Movement)(t)·(1−α)

Threshold(t+1)=Power_(Average)(t+1)+PeakDetectionMargin

After every pass, the power used to move the carriage along the scanaxis may be evaluated. If a threshold power increase is detected duringa pass, the printing may be stopped and the damage evaluation processmay be started. If during the pass the power increase does not reach,the expected power for the following movement may be updated based onthe above equations.

The decay filter may eliminate power variations which do not exceed athreshold amount. The threshold may be set according to the secondequation above. As shown, the threshold may be set based on currentexpected power along with a margin for error to avoid false positives.

The expected power may change over the life of the printer, due forexample to an incremental increase in friction over time as a result ofscan axis degradation. Therefore, the expected power may be updatedafter every pass, or every pass where the threshold power variation isnot exceeded.

The expected power may be updated using the decay filter, wherein aweight (α) may be given to the current expectation and another to thelast measurement (1−α). This may smooth the evolution of the update andhelp account for small incremental increases in power usage. α mayalways be between 0 and 1. The closer the weight a is to 1, the lowerthe impact of the current measurement may be on the expectation.

This update pass after pass may allow for a reduction in thePeakDetectionMargin, which in turn may increase the accuracy of thevariation detection and thus damage detection, particularly in the caseof a thin print medium.

In some examples, according to the equations above, in the event a powerincrease beyond the threshold is detected, a may be set to 1 so that themeasured power does not affect the expected power value (firstequation). In this case it is determined that damage to the print mediumhas occurred and therefore these power measurements would be abnormal,such that they should not be included in the normal expected powerestimation.

Conversely, in some examples, when no power increase beyond thethreshold is detected, a may be set to 0 or 0.5, for example, so thatthe subsequent expected power is either based entirely on the previouspass or partly takes the previous pass into account, when determiningthe expected power.

In some examples as shown in FIG. 4, (with S401 to S403 of FIG. 4corresponding to S101 and S103 of FIG. 1) the method may furthercomprise, when the determining indicates that the print medium isdamaged, inspecting S404 the damage with an optical sensor 130 on a nextprint movement. In some examples, the next print movement is the nextprint swath. For example, if it is determined the print medium isdamaged on a first movement from one side of the print medium to theother, the next print movement may be from the other side of the printmedium back to the one side.

An optical sensor 130 may be passed over the print medium to identifyany damage. Based on the inspection carried out by the optical sensor130, a damage report, which may include information such as a type ofdamage (e.g. a fold, wrinkle or tear) and an indication of damageseverity (e.g. a size of the tear), may be sent to the damage determiner120 a, which may carry out corrective measures, such as moving the printmedium forward along the print path or stopping printing altogether.

In some examples inspecting the damage comprises comparing the locationof the sides of the print medium with predetermined locations of theedges of the print zone. The print medium may be guided by guides alongthe print path which may be used to determine the intended location ofthe print medium which may be compared with the actual location of thesides of the print medium upon visual inspection.

In some examples the method may further comprise, when the determiningindicates that the print medium is damaged, determining S405 whether thedamage includes a tear. Some print media may be more inclined to tearand others to wrinkle or fold. It may be determined whether a tear hasoccurred based on the inspection by the optical sensor 130 or by thecharacteristic of the detected power increase and subsequent power usageprofile. For example, a small tear may be characterised by a short powerusage increase, indicative of the amount of time the printer carriageremains in contact with the print medium, whereas a larger tear may becharacterised by a longer power usage increase, which may remainelevated as the print medium is dragged with the printer carriage.

In some examples the method may further comprise, when the damageincludes a tear, determining S406 whether the tear extends over athreshold amount (e.g. width) of the print medium. If the tear extendsover the threshold amount of the print medium S407, stopping printingand capping the printer nozzles. If the tear does not extend over thethreshold amount S408, moving the print medium forward by apredetermined amount along the print path and resuming printing.

The threshold tear amount may be determined based on the material usedas a print medium and the thickness of the material. For example, somematerials have a relatively strong resistance to tearing, even whenalready torn, such as textiles, in which case the threshold amount maybe relatively large. Other materials, such as thin paper, may offerlower resistance to further tearing when already torn and therefore thethreshold amount will be correspondingly lower.

In one example, print medium comprising paper of 18 gsm may be used andan appropriate tear amount threshold may be approximately 30% of theprint medium width. Thus, if a tear is identified however it is lessthan 30% of substrate width, then the print medium may be advanced by aset amount. An optical scan may be performed (again) at this stage toconfirm no tear is present, and printing may continue. This correctiveaction may be useful for example where printing includes continuousprinting of small, repeated patterns/images along an entire length ofprint medium, where the impact of a blank (non-printed) space, due tomoving the print medium on, is less significant. If a tear is over 30%of the width, in this example, then it may be determined, based on themedium type, thickness and tendency to tear further, that moving theprint medium on may simply tear it further, and printing may thereforebe paused for user intervention.

In some examples, as shown in FIG. 5, there is provided a device, forexample a damage determining device 10 a, comprising a power monitor 100a, such as a power meter, to monitor a power increase, during whichpower usage increases by at least a threshold amount over an expectedpower usage during movement of a printer carriage over a print mediumalong a scan axis. The damage determining device 10 a may be included aspart of a printer carriage or maybe a separate device to the printercarriage. The device may further comprise a locator 110 a to detect alocation of the printer carriage at the time of the detected powerincrease. The device may further comprise a damage determiner 120 a todetermine, based on the detected location of the printer carriage,whether the print medium is damaged. The device may further comprise anoptical sensor 130, to carry out a visual inspection of the printmedium, when the damage determiner 120 a determines that the printmedium is damaged.

In some examples as shown in FIGS. 6a and 6b the power usage profileduring normal printing, shown in FIG. 6a , may include various powerusage spikes or peaks. However, this power usage profile during normalprinting may be compared with the power usage profile when the printercarriage contacts the printing medium which may produce the power usageprofile as shown in FIG. 6b . The variation between the two profiles maybe used to determine whether the print medium has been damaged or not.

Taking the examples shown in FIGS. 6a and 6b , in FIG. 6a , during aregular movement, a deviation of +−1% around the mean may be observed.In FIG. 6b , the peak caused by a crash is 7% over the mean. Therefore,a threshold of 4%, for example, would be appropriate to detect it thecrash while avoiding false positives.

In many print processes printing is ideally carried out in a continuousmanner without interruption. However as print materials become thinner(have a lower gram per square metre value) possible disruptions due toprint medium folding, wrinkling or tearing become more likely. Inaccordance with some examples, downtime and wasted print material ordamage print medium can be minimalised by the above described methodsand devices.

In some examples, there is provided a program which, when executed on acomputer, causes the computer to carry out a process comprising:detecting a power increase, during which power usage increases by atleast a threshold amount over an expected power usage during movement ofa printer carriage over a print medium along a scan axis. The processmay further comprise detecting a location of the printer carriage at thetime of the detected power increase and determining, based on thedetected location of the printer carriage, whether the print medium isdamaged. In some examples, at the end of each printer carriage movement,the power usage over the printer carriage movement is evaluated.

According to the above examples, ink waste and printer damage may beminimised, by identifying print medium damage during printing. Furtherwaste may be reduced by carrying out the appropriate remedial action.Printer downtime may be reduced in cases where the remedial action maybe carried out automatically in response to a determination that printmedium damage has occurred.

Examples in the present disclosure can be provided as methods, systemsor machine readable instructions, such as any combination of software,hardware, firmware or the like. Such machine readable instructions maybe included on a computer readable storage medium (including but is notlimited to disc storage, CD-ROM, optical storage, etc.) having computerreadable program codes therein or thereon.

The present disclosure is described with reference to flow charts and/orblock diagrams of the method, devices and systems according to examplesof the present disclosure. Although the flow diagrams described aboveshow a specific order of execution, the order of execution may differfrom that which is depicted. Blocks described in relation to one flowchart may be combined with those of another flow chart. It shall beunderstood that each flow and/or block in the flow charts and/or blockdiagrams, as well as combinations of the flows and/or diagrams in theflow charts and/or block diagrams can be realized by machine readableinstructions.

The machine readable instructions may, for example, be executed by ageneral purpose computer, a special purpose computer, an embeddedprocessor or processors of other programmable data processing devices torealize the functions described in the description and diagrams. Inparticular, a processor or processing apparatus may execute the machinereadable instructions. Thus functional modules of the apparatus anddevices may be implemented by a processor executing machine readableinstructions stored in a memory, or a processor operating in accordancewith instructions embedded in logic circuitry. The term ‘processor’ isto be interpreted broadly to include a CPU, processing unit, ASIC, logicunit, or programmable gate array etc. The methods and functional modulesmay all be performed by a single processor or divided amongst severalprocessors.

Such machine readable instructions may also be stored in a computerreadable storage that can guide the computer or other programmable dataprocessing devices to operate in a specific mode.

Such machine readable instructions may also be loaded onto a computer orother programmable data processing devices, so that the computer orother programmable data processing devices perform a series ofoperations to produce computer-implemented processing, thus theinstructions executed on the computer or other programmable devicesrealize functions specified by flow(s) in the flow charts and/orblock(s) in the block diagrams.

Further, the teachings herein may be implemented in the form of acomputer software product, the computer software product being stored ina storage medium and comprising a plurality of instructions for making acomputer device implement the methods recited in the examples of thepresent disclosure.

While the method, apparatus and related aspects have been described withreference to certain examples, various modifications, changes,omissions, and substitutions can be made without departing from thespirit of the present disclosure. It is intended, therefore, that themethod, apparatus and related aspects be limited only by the scope ofthe following claims and their equivalents. It should be noted that theabove-mentioned examples illustrate rather than limit what is describedherein, and that those skilled in the art will be able to design manyalternative implementations without departing from the scope of theappended claims.

The word “comprising” does not exclude the presence of elements otherthan those listed in a claim, “a” or “an” does not exclude a plurality,and a single processor or other unit may fulfil the functions of severalunits recited in the claims.

The features of any dependent claim may be combined with the features ofany of the independent claims or other dependent claims.

1. A method comprising: detecting a power increase, during which powerusage increases by at least a threshold amount over an expected powerusage during movement of a printer carriage over a print medium along ascan axis; detecting a location of the printer carriage at a time of thedetected power usage increase; and determining, based on the detectedlocation of the printer carriage, whether the print medium is damaged.2. The method according to claim 1, wherein the power usage is monitoredduring movement of the printer carriage and linked to the position ofthe printer carriage during the movement.
 3. The method according toclaim 2, further comprising, when the position of the printer carriagecorresponds to an edge of a print zone at the time of the detected powerusage increase, determining that the print medium is damaged.
 4. Themethod according to claim 1, further comprising, at the end of eachprinter carriage movement, evaluating the power usage over the printercarriage movement.
 5. The method according to claim 4, furthercomprising, based on the power usage evaluation, determining whether anincrease in friction is detected during printer carriage movement. 6.The method according to claim 1, further comprising applying a decayfilter to the expected power usage to adjust the threshold power usageincrease amount.
 7. The method according to claim 1, further comprising,when the determining indicates that the print medium is damaged,inspecting the damage with an optical sensor on a next print movement.8. The method according to claim 7, wherein inspecting the damagecomprises comparing the location of sides of the print medium withpredetermined locations of sides of a print zone.
 9. The methodaccording to claim 1, further comprising, when the determining indicatesthat the print medium is damaged, determining whether the damageincludes a tear.
 10. The method according to claim 9, furthercomprising, when the damage includes a tear, if the tear extends over athreshold width of the print medium, stopping printing and cappingprinter nozzles.
 11. The method according to claim 9, furthercomprising, when the damage includes a tear, if the tear does not extendover the threshold amount, moving the print medium by a predeterminedamount along the print path and resuming printing.
 12. A devicecomprising: a power monitor to detect a power increase, during whichpower usage increases by at least a threshold amount over an expectedpower usage during movement of a printer carriage over a print mediumalong a scan axis; a locator to detect a location of the printercarriage at the time of the detected power increase; and a damagedeterminer to determine, based on the detected location of the printercarriage, whether the print medium is damaged.
 13. The device accordingto claim 12, further comprising: an optical sensor to inspect printmedium damage.
 14. A program which, when executed on a computer, causesthe computer to carry out a process comprising: detecting a powerincrease, during which power usage increases by at least a thresholdamount over an expected power usage during movement of a printercarriage over a print medium along a scan axis; detecting a location ofthe printer carriage at the time of the detected power increase; anddetermining, based on the detected location of the printer carriage,whether the print medium is damaged.
 15. The program according to claim14, wherein, at the end of each printer carriage movement, the powerusage over the printer carriage movement is evaluated.